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SAW Finger Pair

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Chloe Allison
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In this tutorial we will learn how to simulate a SAW finger pair.  We will analyse the impedance and mode shapes of the design.

You will learn:

  • The basic simulation workflow in OnScale Designer
  • How to set up a 3D model
  • How to create a simple geometry
  • How to edit material properties
  • How to display and post-process results

What is a SAW?: Surface acoustic wave (SAW) filters utilise interdigital transducers on a piezoelectric substrate, where an input transducer converts an electrical signal to an acoustic wave. The propagated mechanical energy is converted back to an electrical signal at the output; the output of the filter is dependent on the frequency response of the device.

Model Definition

model.png

Model Geometry

Characteristics of the model

Model:

SAW

Mesh Size:

15 elements per wavelength

Analysis Time:

20 us

Output Results:

- Impedance

Material Data

Name

Code Name

Density 

Bulk Velocity 

Shear Velocity

Poling

PZT4

pzt4

7500 kg.m-3

-

-

X+

Aluminium

alum

2690 kg.m-3

6306 ms-1

3114 ms-1

-

Silicon, Generic

si

2330 kg.m-3

7526 ms-1

4346 ms-1

-
 

Note: These materials were taken from the Project Materials Database. 

Why This Simulation?

Simulating full 3D SAWs can be time consuming and expensive, so instead initially simulating a saw finger pair can give the user useful information on the design. SAW devices are usually made up of many of these pairs which create the interdigital transducers (IDTs) and the design of these IDTs affects the device performance. It is easy to create a full 3D SAW from this example by using OnScale's patterning feature to pattern out this SAW finger pair.

The Simulation Process

Let's go through the step by step tutorial and see how to simulate a SAW finger pair in OnScale!

Step 1 - Create a New Project

Open up OnScale in Designer Mode. The first step is to create a new project.

  1. In the Home tab of the ribbon, click New Project. The New Project window shows.
  2. Type a name for the project.
  3. If desired, change the save location and/or project file name by clicking … beside Project File.
  4. For Analysis, select Mechanical Dynamic.
  5. For Model Type, select 2D Model.
  6. Select the Advanced checkbox.
  7. For Distance, select μm.
  8. Click OK.

new_project.png

Step 2 - Set the Frequency of Interest

First we will specify the frequency of interest.

  1. Select Project Settings in the Model Tree
  2. Expand the Frequency of Interest property
  3. Tick the box
  4. Enter a value of 1e9
  5. Expand the Frequency of Damping property
  6. Tick the box
  7. Enter a value of 1e9
project_settings.png

Step 3 - Add the Materials from the Material DB

The second step is to add the required materials for the SAW finger pair to the Project Materials database. To open Project Materials database go to Home tab > Materials > Project Materials.

PZT4

Add piezoelectric material.

  1. Expand the 'Piezoelectric' materials dropdown
  2. Double click on 'PZT4 Generic - pzt4' to add it to Project Materials
  3. Expand pzt4
  4. Expand 'Piezoelectric'
  5. Changing 'Poling' dropdown to Z+
add_pzt.png

Alum

Add aluminium material.

  1. Expand the 'Metal' materials dropdown
  2. Double click on 'Aluminium (damping v. low) - alum' to add it to Project Materials
add_alum.png

Aluminium 2

Create a second aluminium material.

  1. Right click on 'alum' and select Copy
  2. Set Material name to alum2
  3. Select OK
add_alum2.png

Silicon

Add silicon material.

  1. Expand the 'Misc' materials dropdown
  2. Double click on 'Silicon, generic - si' to add it to Project Materials
  3. Select Done
add_si.png

Create Basic Geometric Shapes

We will make use of the geometric primitive shapes available in OnScale to build the SAW finger pair.

Substrate

We will start by creating the substrate of the SAW. 

  1. Select Cuboid button
  2. Select primitive_1
  3. Set the Material property of primitive_1 to si
  4. Set the X End property to 50
  5. Set the Y End property to 2
  6. Set the Z End property to 10

Note: You can right click in the workspace and select Reset View to snap the view to the geometry.

add_substrate.png

Piezo

Next we will add another cuboid to create the piezo.

  1. Right click primitive_1 and select Duplicate Selection
  2. Set the Material property of primitive_2 to pzt4
  3. Set Z Begin property of to 10
  4. Set Z End property of to 15
add_piezo.png

Finger 1

Next we will add a polyhedron to represent the first finger.

  1. Select Polyhedron button
  2. Select primitive_3
  3. Set the Material property of primitive_3 to alum
  4. Set Z Begin and Z End property to 15 and 15.2 respectively
  5. Set Number of Points property of primitive_3 to 8
  6. Set Point 1 X and Y coordinates to 0 and 0 respectively
  7. Set Point 2 X and Y coordinates to 0 and 2 respectively
  8. Set Point 3 X and Y coordinates to 10 and 2 respectively
  9. Set Point 4 X and Y coordinates to 10 and 1.8 respectively
  10. Set Point 5 X and Y coordinates to 35 and 1.8 respectively
  11. Set Point 6 X and Y coordinates to 35 and 1.2 respectively
  12. Set Point 7 X and Y coordinates to 10 and 1.2 respectively
  13. Set Point 8 X and Y coordinates to 10 and 0 respectively
add_finger1.png

Finger 2

Next we will add a polyhedron to represent the second finger.

  1. Select Polyhedron button
  2. Select primitive_4
  3. Set the Material property of primitive_4 to alum
  4. Set Z Begin and Z End property to 15 and 15.2 respectively
  5. Set Number of Points property of primitive_3 to 8
  6. Set Point 1 X and Y coordinates to 50 and 0 respectively
  7. Set Point 2 X and Y coordinates to 40 and 0 respectively
  8. Set Point 3 X and Y coordinates to 40 and 0.2 respectively
  9. Set Point 4 X and Y coordinates to 15 and 0.2 respectively
  10. Set Point 5 X and Y coordinates to 15 and 0.8 respectively
  11. Set Point 6 X and Y coordinates to 40 and 0.8 respectively
  12. Set Point 7 X and Y coordinates to 40 and 2 respectively
  13. Set Point 8 X and Y coordinates to 50 and 2 respectively

add_finger2.png

Step 5 - Define a Time Function

The next step is to add a drive function. We will use a Ricker Wavelet time function with a frequency of 1 GHz.

  1. Click '+' to open the Drive Function dialogue
  2. Change function type from Sinusoidal to Ricker Wavelet
  3. Set Drive Frequency to 1e9
  4. Click Insert to close the window. A record called timefunc_1 will be added to the Model Tree.
time_func.png

Step 6 - Choose The Right Mesh Size

It is time to set up the meshing of the model. 

  1. Expand Model and Mesh in the Model Tree
  2. Select Configuration
  3. Set Definitions to Wavelength Based
  4. Set Elements per Wavelength to 15
mesh.png

Step 7 - Create Voltage Loads Between Electrodes and Piezo

We will now create loads on each finger.

Create Load 1

  1. In the Model Tree, expand Boundary Conditions and then, beside Loads, click +.
  2. For Creation Mode, select Geometry Interface.
  3. For Geometry, select primitive_2 (pzt4) or click it in the model.
  4. For Interfacing Item, select primitive_3 (alum).
  5. For Load Type, select Voltage.
  6. For Area Scaling, type 1.
  7. For Termination, select timefunc_1.
  8. Click Create Load.
add_load1.png

Create Load 2

The Load Definition window should still be open.

  1. For Geometry, select primitive_4 (alum2) or click it in the model.
  2. For Interfacing Item, select primitive_2 (pzt4).
  3. For Termination, select Ground.
  4. Click Create Load.
load_2.png

Step 8 - Define the Boundary Conditions

We can leave the boundary conditions as they are defaulted - Free. in all directions

Step 10 - Define the Type of Analysis 

We will now set the model simulation time to be 20 us seconds

  1. Click Analysis 
  2. Change Simulation Run Time to 2e-5
analysis_time.png

Step 11 - Define the Simulation Output Results

We will now define an output so we are able to see the Y velocity in the model.

  1. Click '+' to create a new output
  2. Set Output Type to Field Data
  3. Set Array Type to Velocity
  4. Set Array Component to Y
  5. Set Field Type to Maximum
output.png

Step 12 - Run the Simulation on the Cloud

At this point the model is completely set up and it can now be run on the cloud.

  1. Click Run on Cloud 
  2. Select Estimate 
  3. Change number of CPUs to 16
  4. Select Run
run_on_cloud.png

How to Get the Simulation Results?

Once the simulation has finished, the results are available in your storage to download.

  1. Click the Storage button to open the cloud storage
  2. Select your job from the dropdown menu
  3. Expand the simulation folder and CTRL + select the *.flxdato & *.flxhst file
  4. Select Download > Download Selected
download.png

Choose an appropriate save location and close the cloud storage.

Step 13 - Check the Simulation Results

Switch to the Post Processor 

  1. Click this icon to access the Post Processor to analyse simulation results
pp.png

Open Results

  1. Click File Explorer
  2. Expand the job simulation folder
  3. Double click the *.flxdato file to open the field data results
  4. Double click the *.flxhst file to open the time history results
open_results.png

Plot Charge

  1. From Results Manager, double click 'pize load_1: Charge' to plot charge on first finger
plot_charge.png

Plot Maximum Y Velocity

  1. From Results Manager, double click 'yvmax' to plot maximum Y velocity
  2. Select Continue
  3. Click and drag in the Post Processor to rotate the model
plot_yvel_max.png

Try for Yourself 

Now that we have introduced you to the tutorial, try have a play around with some of the settings, add some other outputs, or use this model as a starting point of your own.

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